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:''See Ricci calculus and Van der Waerden notation for the notation.'' In quantum field theory, the nonlinear Dirac equation is a model of self-interacting Dirac fermions. This model is widely considered in quantum physics as a toy model of self-interacting electrons.〔 〕 The nonlinear Dirac equation appears in the Einstein-Cartan-Sciama-Kibble theory of gravity, which extends general relativity to matter with intrinsic angular momentum (spin).〔Dennis W. Sciama, ("The physical structure of general relativity" ). Rev. Mod. Phys. 36, 463-469 (1964).〕〔Tom W. B. Kibble, ("Lorentz invariance and the gravitational field" ). J. Math. Phys. 2, 212-221 (1961).〕 This theory removes a constraint of the symmetry of the affine connection and treats its antisymmetric part, the torsion tensor, as a variable in varying the action. In the resulting field equations, the torsion tensor is a homogeneous, linear function of the spin tensor. The minimal coupling between torsion and Dirac spinors thus generates an axial-axial, spin–spin interaction in fermionic matter, which becomes significant only at extremely high densities. Consequently, the Dirac equation becomes nonlinear (cubic) in the spinor field, which causes fermions to be spatially extended and may remove the ultraviolet divergence in quantum field theory. ==Models== Two common examples are the massive Thirring model and the Soler model. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nonlinear Dirac equation」の詳細全文を読む スポンサード リンク
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